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Metric surface finish symbols

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Q. I am trying to find out what the symbol "N9"for a finish requirement converts to in Ra.

Thanks

Paul Sawiski
machining operations - Avon, Massachusetts, USA


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A. Roughness grade N9 = 6.3 Ra (in micro meter, which is equivalent to 250 Ra (in micro inches)

Regards,

Niranjan S. Kulkarni
- India


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Q. I AM LOOKING FOR A CHART FOR ALL OF THE ROUGHNESS IN THE N GRADES. N5,N6,N7 ETC.

MEL WIGTON
- DENISON, TEXAS


(2006)

Q. What is the inch equivalent of metric 3.2 surface finish?
Is there a chart for metric or conversion?

Dean Edward Peters
fabricating - Lewisville, Texas


(2006)

A. 3.2µm (micrometer) is equivalent to 125 µin (128 µin to be exact) or Grade N8
It is customary to convert metric roughness to imperial roughness by multiplying 40 to the metric roughness
So:
3.2 µm * 40 µin/um = 128 µin

Ed Chan
- Waterloo, On, Canada


August 12, 2008

Q. Could you tell me what N7 in surface finish is in inch.

Jack Banks
- Cotopaxi, Colorado USA


August 14, 2008

A. Hi. The chart that Mel and Jack are looking for is on letter 7560.

Regards,

Ted Mooney   Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey

January 4, 2013

Q. What metric standard defines the "N" series surface roughness. Has the standard 1.6 roughness callout been phased out to read N7?

Paul Cunningham
- Fremont, California

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